Comment by spwa4

You mean ZIP?

Zip has 2 tricks: First, compression is per-file, allowing extraction of single files without decompressing anything else.

Second, the "directory" is at the end, not the beginning, and ends in the offset of the beginning of the directory. Meaning 2 disk seeks (matters even on SSDs) and you can show the user all files.

Then, you know exactly what bytes are what file and everything's fast. Second, you can easily take off the directory from the zip file, allowing new files to be added without modifying the rest of the file, which can be extended to allow for arbitrary modification of the contents, although you may need to "defragment" the file.

And I believe, encryption is also per-file. Meaning to decrypt a file you need both the password and the directory entry, which means that if you delete a file, and rewrite just the directory, the data is unrecoverable without requiring a total rewrite of the bytes.